Production of volatile dienes by enzymatic dehydration of light alkenols

ABSTRACT

Described is a method for generating conjugated dienes through a biological process. More specifically, the application describes a method for producing conjugated dienes (for example butadiene, isoprene or dimethylbutadiene) from light alkenols via enzymatic dehydration, in particular by making use of an alkenol dehydratase.

This Application is a continuation of Ser. No. 14/195,738, filed on Mar.3, 2014, which is a continuation of Ser. No. 13/957,782, filed on Aug.2, 2013, which is a continuation of EP 12 18 2270.4 which was filed onAug. 29, 2012. The entire contents of Ser. No. 14/195,738, 13/957,482and EP 12 18 2270.4 are hereby incorporated by reference in theirentirety.

The present invention relates to a method for generating conjugateddienes, in particular volatile dienes, through a biological process.More specifically, the invention relates to a method for producingbutadiene, isoprene or dimethylbutadiene from light alkenols viaenzymatic dehydration, in particular by making use of an alkenoldehydratase.

Conjugated dienes, e.g. 1,3-dienes such as butadiene or isoprene, areimportant molecules for the industry. Isoprene (2-methyl-1,3-butadiene)is a conjugated diene with the formula C₅H₈. It, is a key compound forthe tire industry, and also has many applications in the adhesives. Itis produced chemically using several routes:

-   -   Extractive distillation from oil (C5 cut)    -   Dehydrogenation of iso-amylene    -   Double dehydrogenation of isopentane    -   Reaction of isobutene and formaldehyde    -   Reaction of acetone and acetylene    -   Propylene dimerization

WO 2009/076676 reports a metabolic pathway to isoprene. The pathway isbased on the dephosphorylation-dehydration of downstream intermediatesin the mevalonate pathway, i.e. isoprenyl-pyrophosphate orprenyl-pyrophosphate. This process has the drawback of requiring goingthrough the whole mevalonate pathway: double phosphorylation ofmevalonate, followed by a decarboxylation-dehydration intoisoprenyl-pyrophosphate, further isomerised into prenyl-pyrophosphate,and finally double dephosphorylation/dehydration into isoprene.

Butadiene (1,3-butadiene) is a conjugated diene with the formula C₄H₆.It is an important industrial chemical used as a monomer in theproduction of synthetic rubber, nylon, ABS(Acrylonitrile-butadiene-styrene), plastics, latex. There existdifferent possibilities to produce butadiene. Butadiene is, for example,produced as a by product of the steam cracking process used to produceethylene and other olefins. In this process butadiene occurs in the C4stream and is normally isolated from other byproducts by extraction intoa polar aprotic solvent, such as acetonitrile, from which it is thenstripped. Butadiene can also be produced by the catalyticdehydrogenation of normal butane or it can be produced from ethanol. Inthe latter case, two different processes are in use. In a single-stepprocess, ethanol is converted to butadiene, hydrogen and water at400-450° C. over a metal oxide catalyst (Kirshenbaum, I. (1978),Butadiene. In M. Grayson (Ed.), Encyclopedia of Chemical Technology, 3rded., vol. 4, pp. 313-337. New York: John Wiley & Sons). In a two-stepprocess, ethanol is oxidized to acetaldehyde which reacts withadditional ethanol over a tantalum-promoted porous silica catalyst at325-350° C. to yield butadiene (Kirshenbaum, I. (1978), loc cit.).Butadiene can also be produced by catalytic dehydrogenation of normalbutenes.

For the past two decades, genetic engineering technologies have madepossible the modification of the metabolism of micro-organisms, andhence their use to produce key substances which they would otherwiseproduce at a low yield. By enhancing naturally occurring metabolicpathways, these technologies open up new ways to bio-produce numerouscompounds of industrial relevance. Several industrial compounds such asamino-acids for animal feed, biodegradable plastics or textile fibresare now routinely produced using genetically modified organisms.

There is still a need to provide environmentally friendly, costefficient and simple methods for producing the above-mentionedcompounds.

The present application addresses this need by the provision of theembodiments as specified in the claims.

The present invention is based on the design of a novel biocatalyst forthe synthesis of volatile diene compounds, in particular conjugateddienes such as 1,3-dienes, based on the conversion of light alkenols, inparticular by the enzymatic dehydration of light alkenols. The inventionis based on the demonstration that said conversion can be carried outbiologically by using an enzyme catalyzing a dehydration reaction. Theinvention can be implemented in vitro, in cell-free systems, or by usingorganisms, in particular microorganisms. The invention also relates tothe production of conjugated dienes such as 1,3-dienes from a carbonsource, and particularly a carbohydrate (in particular glucose), apolyol (in particular glycerol), a biodegradable polymer (in particularstarch, cellulose, poly-3-hydroxyalkanoate) the carbon source beingconverted by a microorganism to a light alkenol, which is then convertedto a conjugated diene such as a 1,3-diene.

More specifically, the invention relates to a method for producing aconjugated diene characterized in that it comprises a step ofenzymatically converting a compound responding to the general formulaC_(n)H_(2n)O into C_(n)H_(2n-2)+H₂O, with 3<n<7, by making use of analkenol dehydratase. The conversion is a dehydration.

A compound responding to the formula C_(n)H_(2n)O, with 3<n<7, isreferred to in the context of the present invention as a light alkenol.In one preferred embodiment n is 4. In this case, the light alkenol tobe used as a substrate in the method according to the invention respondsto the formula C₄H₈O. Compounds which respond to this formula arebut-2-en-1-ol (crotyl alcohol), but-3-en-2-ol and but-3-en-1-ol(isocrotyl alcohol). The diene which results from the conversion ofthese compounds according to the method of the present invention isbutadiene. In a particularly preferred embodiment the light alkenol usedas a substrate in the method according to the invention is but-2-en-1-ol(crotyl alcohol) or but-3-en-2-ol and the produced diene is butadiene.

In another preferred embodiment n is 5. In this case, the light alkenolto be used as a substrate in the method according to the inventionresponds to the formula C₅H₁₀O. Compounds which respond to this formulaare 2-methylbut-2-en-1-ol, 3-methylbut-2-en-1-ol (prenol), 3-methylbut-3-en-2-ol, 2-methylbut-3-en-2-ol, 2-methylbut-3-en-1-ol and3-methylbut-3-en-1-ol (isoprenol). The diene which results from theconversion of these compounds according to the method of the presentinvention is isoprene. In a particularly preferred embodiment the lightalkenol used as a substrate in the method according to the invention is3-methylbut-2-en-1-ol (prenol) or 2-methylbut-3-en-2-ol and the produceddiene is isoprene.

In another preferred embodiment n is 6. In this case, the light alkenolto be used as a substrate in the method according to the inventionresponds to the formula C₆H₁₂0. Compounds which respond to this formulaare 2,3-dimethylbut-2-en-1-ol, 2,3-dimethylbut-3-en-2-ol and2,3-dimethylbut-3-en-1-ol. The diene which results from the conversionof these compounds according to the method of the present invention isdimethyl-butadiene.

The compounds responding to the general formula C_(n)H_(2n)O, with3<n<7, can be subdivided into three groups, namely into

-   (i) primary allyl alcohols (PRA) of the formula I:

-   (ii) secondary or tertiary allyl alcohols (STA) of the formula II:

-   and-   (iiI) primary homoallyl alcohols (PHA) of the formula III:

wherein R¹ and R² are independently selected from H and CH₃.

In one preferred embodiment, the compound responding to the generalformula C_(n)H_(2n)O, with 3<n<7, is a primary allyl alcohol (PRA) ofthe formula I:

-   wherein R¹ and R² are independently selected from H and CH₃.    Compounds responding to this formula are but-2-en-1-ol (crotyl    alcohol), 2-methylbut-2-en-1-ol, 3-methylbut-2-en-1-ol (prenol) and    2,3-dimethylbut-2-en-1-ol (see FIG. 1). In one preferred embodiment,    the primary allyl alcohol is but-2-en-1-ol (crotyl alcohol) and the    produced diene is butadiene. In another preferred embodiment, the    primary allyl alcohol is 3-methylbut-2-en-1-ol (prenol) and the    produced diene is isoprene.

In another preferred embodiment, the compound responding to the generalformula C_(n)H_(2n)O, with 3<n<7, is a secondary or tertiary allylalcohol (STA) of the formula II:

-   wherein R¹ and R² are independently selected from H and CH₃.    Compounds responding to this formula are but-3-en-2-ol,    3-methylbut-3-en-2-ol, 2-methylbut-3-en-2-ol and    2,3-dimethylbut-3-en-2-ol (see FIG. 2).

In one preferred embodiment, the STA is but-3-en-2-ol and the produceddiene is butadiene. In another preferred embodiment, the STA is2-methylbut-3-en-2-ol and the produced diene is isoprene.

In a further preferred embodiment, the compound responding to thegeneral formula C_(n)H_(2n)O, with 3<n<7, is a primary homoallyl alcohol(PHA) of the formula III:

-   wherein R¹ and R² are independently selected from H and CH₃.    Compounds responding to this formula are but-3-en-1-ol (isocrotyl    alcohol), 2-methylbut-3-en-1-ol, 3-methylbut-3-en-1-ol (isoprenol)    and 2,3-dimethylbut-3-en-1-ol (see FIG. 3). In one preferred    embodiment, the homoallyl alcohol is 3-methylbut-3-en-1-ol    (isoprenol) and the produced diene is isoprene.

FIG. 4 gives a schematic overview over the conversion of the abovementioned PRA, PHA and STA compounds into a conjugated diene accordingto the method of the present invention.

If reference is made in the context of the present invention to acompound of which there exist stereoisomers, e.g. because of Z/Einversions at the sp2 C═C double bonds or because of R/S inversions atthe chiral sp3 C centers, all these stereoisomers are encompassed byreference to such a compound. For example, the mention of but-2-en-1-ol(crotyl alcohol) refers to the cis (Z) as well as to the trans (E)stereoisomer and the mention of 3-methylbut-3-en-2-ol refers to both theR and S isomer.

As described above, the method according to the present invention ischaracterized in that the conversion of the compound responding to thegeneral formula C_(n)H_(2n)O into C_(n)H_(2n-2)+H₂O, with 3<n<7, isachieved by using an alkenol dehydratase. An alkenol dehydratase is anenzyme which can dehydrate an alkenol, preferably, it is an enzyme whichcan dehydrate at least one compound responding to the general formulaC_(n)H_(2n)O, with 3<n<7, and wherein the product of the reaction isC_(n)H_(2n-2)+H₂O. This activity can be measured in assays as describedin the appended Examples. An example of an alkenol dehydratase to beemployed in a method according to the present invention is the alkenoldehydratase which has been designated “linalool dehydratase-isomerase”and which has been identified in Castellaniella defragrans (formerlyAlcaligenes defragrans) strain 65Phen (Brodkorb et al., J. Biol. Chem.285 (2010), 30436-30442). Linalool dehydratase-isomerase is abifunctional enzyme which is involved in the anaerobic degradation ofmonoterpenes. The native enzyme has been found to have a molecular massof 160 kDa and is assumed to be a homotetramer of 40 kDa subunits. Theenzyme catalyzes in vitro two reactions in both directions depending onthe thermodynamic driving forces. On the one hand, the enzyme catalyzesthe isomerisation of the primary allylalcohol geraniol into itsstereoisomer linalool which bears a tertiary allyl alcohol motif. On theother hand, the enzyme catalyzes the water secession (dehydration) fromthe tertiary alcohol linalool to the corresponding acyclic monoterpenebeta-myrcene, a molecule bearing a conjugated diene motif. FIG. 5 givesan overview of the reactions catalyzed by linalool dehydratase-isomerasein vitro under anaerobic conditions. In Castellaniella defragrans theprotein is expressed as a precursor protein with a signal peptide for aperiplasmatic location which is cleaved after transport through themembrane. The enzyme is classified as EC 4.2.1.127. A linalooldehydratase-isomerase has the capacity to catalyze the followingreaction under anaerobic conditions:Linalool<=>myrcene+H₂O

This activity can, e.g., be measured with an assay as described inBrodkorb et al. (loc. cit.). In such an assay, vials are prewarmed at35° C., anoxic protein solution is transferred into the vials and DTT isadded to 2 mM. The reaction mixtures are sealed with a butyl septum andthe headspace is flushed with CO₂/N₂ (10/90 (v/v)). The reaction isstarted by adding a distinct concentration of linalool and incubated at35° C. The conversion of linalool into myrcene is assessed byinvestigating the production of myrcene, e.g. by gas chromatography.

In a preferred embodiment, a linalool dehydratase-isomerase also has thecapacity to catalyze the isomerisation of geraniol into linalool underanaerobic conditions:Geraniol<=>linalool

This activity can, e.g., be measured with an assay as described inBrodkorb et al. (loc. cit.). In such an assay, vials are prewarmed at35° C., anoxic protein solution is transferred into the vials and DTT isadded to 2 mM. The reaction mixtures are sealed with a butyl septum andthe headspace is flushed with CO₂/N₂ (10/90 (v/v)). The reaction isstarted by adding a distinct concentration of geraniol and incubated at35° C. The conversion of geraniol into linalool is assessed byinvestigating the production of myrcene, i.e. the product of the secondreaction catalyzed by the enzyme, e.g. by gas chromatography.

Geraniol, linalool and myrcene are acyclic C₁₀-terpenoids produced byplants, belonging to the class of allylalcohols and hydrocarbons,respectively. Lüddecke and Harder (Z. Naturforsch. 66c (2011), 409-412)reported on a high substrate specificity of linalooldehydratase-isomerase. The inventors now surprisingly found thatlinalool dehydratase-isomerase can act on compounds of the formulaC_(n)H_(2n)O, with 3<n<7, and can convert them into conjugated dienes.In the appended Examples this is shown for the conversion ofbut-2-en-1-ol (crotyl alcohol) into butadiene, of but-3-en-2-ol intobutadiene, of 3-methylbut-2-en-1-ol (prenol) into isoprene, of3-methylbut-3-en-1-ol (isoprenol) into isoprene and of2-methylbut-3-en-2-ol into isoprene. Thus, the present inventors couldshow that linalool dehydratase-isomerase can unexpectedly also convertalkenols which are much shorter than its natural substrates despite ofthe reported high substrate specificity.

An example of a sequence of an alkenol dehydratase which can be employedin the method according to the present invention is given in SEQ ID NO:1 (FIG. 6). A sequence for an alkenol dehydratase is also accessible inthe UniProtKB/TrEMBL database under accession number E1XUJ2. Thesesequences represent an alkenol dehydratase which is classified as alinalool dehydratase-isomerase. In a preferred embodiment the methodaccording to the present invention makes use of an alkenol dehydratasecomprising the amino acid sequence shown in SEQ ID NO: 1 or a sequencewhich is at least x % identical to SEQ ID NO: 1 and which is able tocatalyze the conversion of a compound responding to the general formulaC_(n)H_(2n)O into C_(n)H_(2n-2)+H₂O, with 3<n<7, with x being an integerbetween 30 and 100, preferably 35, 40, 45, 50, 55, 60, 65, 70, 75, 80,85, 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99.

The term “alkenol dehydratase” as used in the present inventiontherefore refers to an enzyme which shows the above indicated degree ofsequence identity with SEQ ID NO:1 and which can catalyze the conversionof a compound responding to the general formula C_(n)H_(2n)O intoC_(n)H_(2n-2)+H₂O, with 3<n<7. By using the sequence of SEQ ID NO:1 orcorresponding encoding nucleotide sequences, it is possible for theskilled person to identify further alkenol dehydratases which cancatalyze the above indicated conversion.

Preferably, the degree of identity is determined by comparing therespective sequence with the amino acid sequence of SEQ ID NO:1. Whenthe sequences which are compared do not have the same length, the degreeof identity preferably either refers to the percentage of amino acidresidues in the shorter sequence which are identical to amino acidresidues in the longer sequence or to the percentage of amino acidresidues in the longer sequence which are identical to amino acidresidues in the shorter sequence. The degree of sequence identity can bedetermined according to methods well known in the art using preferablysuitable computer algorithms such as CLUSTAL.

When using the Clustal analysis method to determine whether a particularsequence is, for instance, 80% identical to a reference sequence defaultsettings may be used or the settings are preferably as follows: Matrix:blosum 30; Open gap penalty: 10.0; Extend gap penalty: 0.05; Delaydivergent: 40; Gap separation distance: 8 for comparisons of amino acidsequences. For nucleotide sequence comparisons, the Extend gap penaltyis preferably set to 5.0.

Preferably, the degree of identity is calculated over the completelength of the sequence.

Moreover, if the term “homology” is used in the context of the presentinvention, this term preferably means “sequence identity”.

As described above, the alkenol dehydratase which is referred to as a“linalool dehydratase-isomerase” identified in Castellaniella defragrans(formerly Alcaligenes defragrans) has a signal peptide ensuringtransport into the periplasmatic space. In a preferred embodiment, themethod according to the present invention employs an enzyme which doesnot show such a signal sequence. It is shown in the Examples thatdisruption of the signal peptide by insertion of a his-tag does nothamper the expression of the enzyme in E. coli and leads to theintracellular production of an active protein.

The alkenol dehydratase, such as a linalool dehydratase-isomerase,employed in the process according to the invention can be a naturallyoccurring alkenol dehydratase or it can be an alkenol dehydratase whichis derived from a naturally occurring alkenol dehydratase such as alinalool dehydratase-isomerase, e.g. by the introduction of mutations orother alterations which, e.g., alter or improve the enzymatic activity,the stability, in particular thermal stability etc.

The term “linalool dehydratase-isomerase” or “a protein/enzyme havingthe activity of a linalool dehydratase-isomerase” in the context of thepresent application also covers enzymes which are derived from alinalool dehydratase-isomerase, which are capable of catalyzing theconversion of a compound responding to the general formula C_(n)H_(2n)Ointo C_(n)H_(2n-2)+H₂O, with 3<n<7, but which only have a low affinityto their natural substrates, i.e. geraniol, linalool and/or myrcene, ordo no longer accept their natural substrates. Such a modification of thepreferred substrate allows to improve the conversion of a compoundresponding to the general formula C_(n)H_(2n)O into C_(n)H_(2n-2)+H₂O,with 3<n<7, and to reduce the production of possibly occurring unwantedby-products. Methods for modifying and/or improving the desiredenzymatic activities of proteins are well-known to the person skilled inthe art and include, e.g., random mutagenesis or site-directedmutagenesis and subsequent selection of enzymes having the desiredproperties or approaches of the so-called “directed evolution”, DNAshuffling or in vivo evolution.

For example, for genetic engineering in prokaryotic cells, a nucleicacid molecule encoding a linalool dehydratase-isomerase can beintroduced into plasmids which permit mutagenesis or sequencemodification by recombination of DNA sequences. Standard methods (seeSambrook and Russell (2001), Molecular Cloning: A Laboratory Manual, CSHPress, Cold Spring Harbor, N.Y., USA) allow base exchanges to beperformed or natural or synthetic sequences to be added. DNA fragmentscan be connected to each other by applying adapters and linkers to thefragments. Moreover, engineering measures which provide suitablerestriction sites or remove surplus DNA or restriction sites can beused. In those cases, in which insertions, deletions or substitutionsare possible, in vitro mutagenesis, “primer repair”, restriction orligation can be used. In general, a sequence analysis, restrictionanalysis and other methods of biochemistry and molecular biology arecarried out as analysis methods. The resulting linalooldehydratase-isomerase variants are then tested for their enzymaticactivity and in particular for their capacity to prefer a compoundresponding to the general formula C_(n)H_(2n)O, with 3<n<7, as asubstrate rather than, e.g. geraniol, linalool and/or myrcene.

Such methods for identifying variants with improved enzymatic propertiesas regards the production of a conjugated diene compound may also becarried out in the presence of a cofactor which allows for a stericand/or electronic complementation in the catalytic site of the enzymedue to the fact that the a compound responding to the general formulaC_(n)H_(2n)O, with 3<n<7, is shorter than the natural substrates.

In a preferred embodiment the alkenol dehydratase employed in a methodaccording to the invention shows a high thermal stability. Such anenzyme can be obtained by routine methods involving, e.g. randomlymutating a nucleic acid sequence encoding an alkenol dehydratase andscreening the obtained mutants for a higher thermal stability.Preferably, the alkenol dehydratase is stable and enzymatically activeat temperatures of 68° C. or higher. Since the boiling point ofdimethylbutadiene is 68° C. at atmospheric pressure, using such anenzyme and carrying out the method according to the invention at atemperature of 68° C. or higher has the advantage that thedimethylbutadiene degasses out of the reaction and can easily berecovered from the gaseous phase.

The modified version of the alkenol dehydratase, e.g. a variantaccepting or preferring a compound responding to the general formulaC_(n)H_(2n)O, with 3<n<7, as a substrate but having a low affinity toits natural substrates or no longer accepting its natural substrates ora variant with a higher thermal stability, may be derived from anaturally occurring alkenol dehydratase, such as a linalooldehydratase-isomerase, or from an already modified, optimized orsynthetically prepared alkenol dehydratase.

The method according to the invention can be carried out in vitro, e.g.in the presence of isolated enzyme or of cell lysates comprising theenzyme or partially purified enzyme preparations. In vitro preferablymeans in a cell-free system.

In one embodiment, the enzyme employed in the method is used in purifiedform to convert a compound responding to the general formulaC_(n)H_(2n)O into C_(n)H_(2n-2)+H₂O, with 3<n<7. However, such a methodmay be costly, since enzyme and substrate production and purificationcosts are high.

Thus, in another preferred embodiment, the enzymes employed in themethod are present in the reaction as a non-purified extract, or else inthe form of non-lysed bacteria, so as to economize on proteinpurification costs. However, the costs associated with such a method maystill be quite high due to the costs of producing and purifying thesubstrates.

In an in vitro reaction the enzymes, native or recombinant, purified ornot, are incubated in the presence of the substrate in physicochemicalconditions allowing the enzymes to be active, and the incubation isallowed to proceed for a sufficient period of time allowing productionof the diene. At the end of the incubation, one optionally measures thepresence of the diene compound by using any detection system known toone of skill in the art such as gas chromatography or colorimetric testsfor measuring the formation such compounds.

In a particularly preferred embodiment of the invention the method iscarried out in vitro and the enzyme is immobilized. Means and methodsfor immobilizing enzymes on different supports are well-known to theperson skilled in the art.

In another preferred embodiment the method according to the invention iscarried out in culture, in the presence of an organism, preferably amicroorganism, producing the enzyme. Thus, in such an embodiment of theinvention, an organism, preferably a microorganism, that produces analkenol dehydratase, such as a linalool dehydratase-isomerase, is used.In a preferred embodiment, the (micro)organism is recombinant in thatthe enzyme produced by the host is heterologous relative to theproduction host. The method can thus be carried out directly in theculture medium, without the need to separate or purify the enzymes. Inan especially advantageous manner, a (micro)organism is used having thenatural or artificial property of endogenously producing a compoundresponding to the general formula C_(n)H_(2n)O, with 3<n<7, and alsoexpressing or overexpressing an alkenol dehydratase, such as a linalooldehydratase-isomerase, natural or modified, so as to produce the dienecompound directly from a carbon source present in solution.

For example, the method according to the invention can be carried out byusing microorganisms which produce a compound responding to the generalformula C_(n)H_(2n)O, with 3<n<7. For example, Perez et al.(Phytochemistry 19 (1980), 183-187) describe enzymes from Citrussinensis which are able to hydrolyze allylic phosphates, e.g. a prenyldiphosphatase (EC 3.1.7.1) which can convert prenol diphosphate intoprenol and diphosphate. Nucleic acid sequences encoding such enzymes canbe introduced into microorganisms which produce the correspondingsubstrate so as to be able to produce prenol. Moreover, Withers et al.(Appl. Environ. Microbiol. 73 (2007), 6277-6283) have described, forexample, E. coli cells which have been engineered with themevalonate-based isopentenyl pyrophosphate biosynthetic pathway andwhich also expressed the nudF gene of Bacillus subtilis strain 6,051.The protein encoded by the nudF gene acts directly on prenyl diphosphateprecursors and leads to the production of isopentenol (isoprenol).

Thus, in one embodiment of the method according to the present inventionit is preferred to use a microorganism which is capable of producing acompound responding to the general formula C_(n)H_(2n)O, with 3<n<7, andwhich has been genetically engineered such that it (over)expresses analkenol dehydratase, said alkenol dehydratase preferably originatingfrom an organism different from the host microorganism. The geneticmodification can consist, e.g. in integrating the corresponding geneencoding the alkenol dehydratase into the chromosome, expressing theenzyme from a plasmid containing a promoter upstream of theenzyme-coding sequence, the promoter and coding sequence preferablyoriginating from different organisms, or any other method known to oneof skill in the art. Alternatively, other bacteria or yeasts may havespecific advantages and can be chosen. For instance, a yeast such asSaccharomyces cerevisiae, an extremophilic bacterium such as Thermusthermophilus, or anaerobic bacteria from the family Clostridiae,microalgae, or photosynthetic bacteria can be used.

It is also conceivable to isolate the genes encoding the proteins whichare responsible for the synthesis of a compound responding to thegeneral formula C_(n)H_(2n)O, with 3<n<7, and to introduce these genesinto another organisms, in particular a microorganism, such as e.g. E.coli, Saccharomyces or Pichia, an extremophilic bacterium such asThermus thermophilus, or anaerobic bacteria from the family Clostridiae,microalgae, or photosynthetic bacteria.

In a preferred embodiment, the (micro)organism) used in the methodaccording to the invention is a (micro)organism which is geneticallymodified so as to contain a nucleic acid molecule encoding an alkenoldehydratase. Such a nucleic acid molecule encoding an alkenoldehydratase as described above can be used alone or as part of a vector.The nucleic acid molecules can further comprise expression controlsequences operably linked to the polynucleotide comprised in the nucleicacid molecule. The term “operatively linked” or “operably linked”, asused throughout the present description, refers to a linkage between oneor more expression control sequences and the coding region in thepolynucleotide to be expressed in such a way that expression is achievedunder conditions compatible with the expression control sequence.

Expression comprises transcription of the heterologous DNA sequence,preferably into a translatable mRNA. Regulatory elements ensuringexpression in fungi as well as in bacteria, are well known to thoseskilled in the art. They encompass promoters, enhancers, terminationsignals, targeting signals and the like. Examples are given furtherbelow in connection with explanations concerning vectors.

Promoters for use in connection with the nucleic acid molecule may behomologous or heterologous with regard to its origin and/or with regardto the gene to be expressed. Suitable promoters are for instancepromoters which lend themselves to constitutive expression. However,promoters which are only activated at a point in time determined byexternal influences can also be used. Artificial and/or chemicallyinducible promoters may be used in this context.

The vectors can further comprise expression control sequences operablylinked to said polynucleotides contained in the vectors. Theseexpression control sequences may be suited to ensure transcription andsynthesis of a translatable RNA in bacteria or fungi.

In addition, it is possible to insert different mutations into thepolynucleotides by methods usual in molecular biology (see for instanceSambrook and Russell (2001), Molecular Cloning: A Laboratory Manual, CSHPress, Cold Spring Harbor, N.Y., USA), leading to the synthesis ofpolypeptides possibly having modified biological properties. Theintroduction of point mutations is conceivable at positions at which amodification of the amino acid sequence for instance influences thebiological activity or the regulation of the polypeptide.

Moreover, mutants possessing a modified substrate or product specificitycan be prepared. Preferably, such mutants show an increased activity.Furthermore, the introduction of mutations into the polynucleotidesencoding an enzyme as defined above allows the gene expression rateand/or the activity of the enzymes encoded by said polynucleotides to beoptimized, e.g. as regards thermal stability.

For genetically modifying bacteria or fungi, the polynucleotidesencoding an enzyme as defined above or parts of these molecules can beintroduced into plasmids which permit mutagenesis or sequencemodification by recombination of DNA sequences. Standard methods (seeSambrook and Russell (2001), Molecular Cloning: A Laboratory Manual, CSHPress, Cold Spring Harbor, N.Y., USA) allow base exchanges to beperformed or natural or synthetic sequences to be added. DNA fragmentscan be connected to each other by applying adapters and linkers to thefragments. Moreover, engineering measures which provide suitablerestriction sites or remove surplus DNA or restriction sites can beused. In those cases, in which insertions, deletions or substitutionsare possible, in vitro mutagenesis, “primer repair”, restriction orligation can be used. In general, a sequence analysis, restrictionanalysis and other methods of biochemistry and molecular biology arecarried out as analysis methods.

The polynucleotide introduced into a (micro)organism is expressed so asto lead to the production of a polypeptide having the activity describedabove. An overview of different expression systems is for instancecontained in Methods in Enzymology 153 (1987), 385-516, in Bitter et al.(Methods in Enzymology 153 (1987), 516-544) and in Sawers et al.(Applied Microbiology and Biotechnology 46 (1996), 1-9), Billman-Jacobe(Current Opinion in Biotechnology 7 (1996), 500-4), Hockney (Trends inBiotechnology 12 (1994), 456-463), Griffiths et al., (Methods inMolecular Biology 75 (1997), 427-440). An overview of yeast expressionsystems is for instance given by Hensing et al. (Antonie van Leuwenhoek67 (1995), 261-279), Bussineau et al. (Developments in BiologicalStandardization 83 (1994), 13-19), Gellissen et al. (Antonie vanLeuwenhoek 62 (1992), 79-93, Fleer (Current Opinion in Biotechnology 3(1992), 486-496), Vedvick (Current Opinion in Biotechnology 2 (1991),742-745) and Buckholz (Bio/Technology 9 (1991), 1067-1072).

Expression vectors have been widely described in the literature. As arule, they contain not only a selection marker gene and areplication-origin ensuring replication in the host selected, but also abacterial or viral promoter, and in most cases a termination signal fortranscription. Between the promoter and the termination signal there isin general at least one restriction site or a polylinker which enablesthe insertion of a coding DNA sequence. The DNA sequence naturallycontrolling the transcription of the corresponding gene can be used asthe promoter sequence, if it is active in the selected host organism.However, this sequence can also be exchanged for other promotersequences. It is possible to use promoters ensuring constitutiveexpression of the gene and inducible promoters which permit a deliberatecontrol of the expression of the gene. Bacterial and viral promotersequences possessing these properties are described in detail in theliterature. Regulatory sequences for the expression in microorganisms(for instance E. coli, S. cerevisiae) are sufficiently described in theliterature. Promoters permitting a particularly high expression of adownstream sequence are for instance the T7 promoter (Studier et al.,Methods in Enzymology 185 (1990), 60-89), lacUV5, trp, trp-lacUV5(DeBoer et al., in Rodriguez and Chamberlin (Eds), Promoters, Structureand Function; Praeger, N.Y., (1982), 462-481; DeBoer et al., Proc. Natl.Acad. Sci. USA (1983), 21-25), Ip1, rac (Boros et al., Gene 42 (1986),97-100). Inducible promoters are preferably used for the synthesis ofpolypeptides. These promoters often lead to higher polypeptide yieldsthan do constitutive promoters. In order to obtain an optimum amount ofpolypeptide, a two-stage process is often used. First, the host cellsare cultured under optimum conditions up to a relatively high celldensity. In the second step, transcription is induced depending on thetype of promoter used. In this regard, a tac promoter is particularlysuitable which can be induced by lactose or IPTG(=isopropyl-β-D-thiogalactopyranoside) (deBoer et al., Proc. Natl. Acad.Sci. USA 80 (1983), 21-25). Termination signals for transcription arealso described in the literature.

The coding region encoding the alkenol dehydratase may be modified inways known to the person skilled in the art. It is, e.g., possible toinsert tags which simplify the purification of the protein such as ahis-tag (see Example 1). Moreover, it is also possible to delete ordisrupt the signal sequence of the enzyme which ensures localization inthe periplasma thereby allowing the protein to be producedintracellularly. It is also possible to attach to the coding region asecretion signal allowing secretion of the protein into the culturemedium.

It is also possible to express the alkenol dehydratase as a fusionprotein in which the alkenol dehydratase is fused to another polypeptidemoiety, e.g. another enzyme. The transformation of the host cell with apolynucleotide or vector according to the invention can be carried outby standard methods, as for instance described in Sambrook and Russell(2001), Molecular Cloning: A Laboratory Manual, CSH Press, Cold SpringHarbor, N.Y., USA; Methods in Yeast Genetics, A Laboratory CourseManual, Cold Spring Harbor Laboratory Press, 1990. The host cell iscultured in nutrient media meeting the requirements of the particularhost cell used, in particular in respect of the pH value, temperature,salt concentration, aeration, antibiotics, vitamins, trace elements etc.

The organisms used in the invention can be prokaryotes or eukaryotes,preferably, they are microorganisms. The term “microorganism” in thecontext of the present invention refers to bacteria, as well as tofungi, such as yeasts, and also to algae and archaea. The term“microorganism” also includes plant cells or animal cells. In aparticular embodiment the microorganisms are bacteria. Preferredbacteria to be employed in the process according to the invention arebacteria of the genus Bacillus, Clostridium, Corynebacterium,Pseudomonas, Zymomonas, Methylobacter or Escherichia. In a particularlypreferred embodiment the bacterium belongs to the genus Escherichia andeven more preferred to the species Escherichia coli. In anotherpreferred embodiment the bacterium belongs to the species Pseudomonasputida or to the species Zymomonas mobilis or to the speciesCorynebacterium glutamicum.

In another preferred embodiment, the microorganisms are recombinantbacteria, preferably of the genus Escherichia, having been modified soas to endogenously produce a compound responding to the general formulaC_(n)H_(2n)O, with 3<n<7, and converting it to a diene compound asdescribed herein above.

The term “microorganism” in the context of the present invention refersto bacteria, as well as to fungi, such as yeasts, and also to algae andarchaea. In one preferred embodiment, the microorganism is a bacterium.In principle any bacterium can be used. Preferred bacteria to beemployed in the process according to the invention are bacteria of thegenus Bacillus, Clostridium, Corynebacterium, Pseudomonas, Zymomonas orEscherichia. In a particularly preferred embodiment the bacteriumbelongs to the genus Escherichia and even more preferred to the speciesEscherichia coli. In another preferred embodiment the bacterium belongsto the species Pseudomonas putida or to the species Zymomonas mobilis orto the species Corynebacterium glutamicum.

In another preferred embodiment the microorganism is a fungus, morepreferably a fungus of the genus Saccharomyces, Schizosaccharomyces,Aspergillus, Trichoderma, Kluyveromyces or Pichia and even morepreferably of the species Saccharomyces cerevisiae, Schizosaccharomycespombe, Aspergillus niger, Trichoderma reesei, Kluyveromyces marxianus,Kluyveromyces lactis or Pichia pastoris.

In a particularly preferred embodiment the microorganism is arecombinant fungus, preferably a yeast producing a compound respondingto the general formula C_(n)H_(2n)O, with 3<n<7, and converting it to adiene compound as described herein above.

In another preferred embodiment, the method according to the inventionmakes use of a photosynthetic microorganism expressing an alkenoldehydratase. Preferably, the microorganism is a photosyntheticbacterium, or a microalgae. Even more preferably such a microorganismhas the natural or artificial property of endogenously producingcompound responding to the general formula C_(n)H_(2n)O, with 3<n<7. Inthis case the microorganism would be capable of producing a dienedirectly from CO₂ present in solution.

In another preferred embodiment the method according to the inventionmakes use of a multicellular organism expressing an alkenol dehydratase.Examples for such organisms are plants or animals.

In one embodiment, the method involves cultivating microorganisms instandard culture conditions (30-37° C. at 1 atm, in a fermenter allowingaerobic growth of the bacteria). Butadiene and isoprene have a boilingpoint of −4° C. and 34° C., respectively, and would already be in agaseous state if a temperature of 34° C. or higher is chosen for thecultivation. In a preferred embodiment, the method involves cultivatingmicroorganisms under non-standard conditions, preferably at a highertemperature to correspond to the culture conditions of thermophilicorganisms. This embodiment has the advantage that even those dieneswhich have a higher boiling point, in particular dimethylbutadiene (witha boiling point of 68° C.) would degas out of the culture and could beeasily collected from the gaseous phase. Thus, in particular in thoseembodiments of the method according to the invention in whichdimethylbutadiene is produced, the microorganism is a thermophilicmicroorganism which can be cultivated at temperatures of 68° C. orhigher.

In a further preferred embodiment, the method according to the inventionmaking use of a microorganism is carried out such that the microorganismis immobilized on a support.

In a further preferred embodiment the method of the invention is carriedout in microaerophilic conditions. This means that the quantity ofinjected air is limiting so as to minimize residual oxygenconcentrations in the gaseous effluents containing the produced dienecompound.

In another preferred embodiment the method according to the invention iscarried out under conditions so that the produced diene is degassing outof the reaction. This has the advantage that the thermodynamicequilibrium of the reaction is shifted toward production of theconjugated diene. It is preferred that the method furthermore comprisesthe step of collecting the gaseous diene. Thus, in a preferredembodiment, the method is carried out in the presence of a system forcollecting the produced diene under gaseous form during the reaction.

In a particular embodiment, the method also comprises detecting theproduced diene (butadiene, isoprene or dimethylbutadiene) which ispresent in the gaseous phase. The presence of the diene to be producedin an environment of air or another gas, even in small amounts, can bedetected by using various techniques and in particular by using gaschromatography systems with infrared or flame ionization detection, orby coupling with mass spectrometry.

The present invention also relates to the use of an organism whichproduces an alkenol dehydratase, such as a linalooldehydratase-isomerase, for the conversion of a compound responding tothe general formula C_(n)H_(2n)O into C_(n)H_(2n-2)+H₂O, with 3<n<7, asdescribed herein above in connection with the method according to theinvention. In a preferred embodiment such an organism is a recombinantorganism in the sense that it is genetically modified due to theintroduction of at least one nucleic acid molecule encoding an alkenoldehydratase, such as a linalool dehydratase-isomerase. Preferably such anucleic acid molecule is heterologous with regard to the organism whichmeans that it does not naturally occur in said organism.

In a preferred embodiment such an organism is an organism which producesa compound responding to the general formula C_(n)H_(2n)O, with 3<n<7.

The present invention also relates to the use of an alkenol dehydratase,such as a linalool dehydratase-isomerase, for the conversion of acompound responding to the general formula C_(n)H_(2n)O intoC_(n)H_(2n-2)+H₂O, with 3<n<7, as described herein above in connectionwith the method according to the invention.

Moreover, the present invention also relates to a composition comprisingan organism which produces an alkenol dehydratase and a compoundresponding to the general formula C_(n)H_(2n)O, with 3<n<7. The presentinvention also relates to a composition comprising an alkenoldehydratase, such as a linalool dehydratase-isomerase, and a compoundresponding to the general formula C_(n)H_(2n)O, with 3<n<7.

As regards the preferred embodiments of the different componentsrecited, the same applies as has been set forth above in connection withthe method according to the invention.

FIG. 1 shows schematically the primary allyl alcohols (PRA) respondingto the general formula C_(n)H_(2n)O, with 3<n<7. In particular shownare: Substrate/Systematic name/Formula/Category/R¹/R²/Product

FIG. 2 shows schematically the secondary and tertiary allyl alcohols(STA) responding to the general formula C_(n)H_(2n)O, with3<n<7.Substrate/Systematic name/Formula/Category/R¹/R²/Product

FIG. 3 shows schematically the primary homoallyl alcohols (PHA)responding to the general formula C_(n)H_(2n)O, with3<n<7.Substrate/Systematic name/Formula/Category/R¹/R²/Product

FIG. 4 shows a schematic overview over the conversion of the abovementioned PRA, PHA and STA compounds into a conjugated diene accordingto the method of the present invention.

FIG. 5 shows an overview of the reactions catalyzed by linalooldehydratase-isomerase.

FIG. 6 shows the amino acid sequence of the linalooldehydratase-isomerase from Castellaniella defragrans (formerlyAlcaligenes defragrans).

FIG. 7 shows the GC/FID chromatograms obtained for enzymatic (black) andenzyme-free (red) assays with 80 mM trans crotyl alcohol after 22 hoursincubation.

FIG. 8 shows the GC/FID chromatograms obtained for enzymatic (black) andenzyme-free (red) assays with 80 mM 3-buten-2-ol after 22 hoursincubation.

FIG. 9 shows the GC/FID chromatograms obtained for enzymatic (black) andenzyme-free (blue) assays with 80 mM isoprenol after 22 hoursincubation.

FIG. 10 shows the GC/FID chromatograms obtained for enzymatic (red) andenzyme-free (black) assays with 80 mM 2-methyl-3-buten-2-ol after 22hours incubation.

Other aspects and advantages of the invention will be described in thefollowing examples, which are given for purposes of illustration and notby way of limitation.

EXAMPLES Example 1 Cloning and Expression in E. coli of the Gene forLinalool Dehydratase-Isomerase

Cloning and Bacterial Culture

The sequence of linalool dehydratase-isomerase inferred from the genomeof Castellaniella defragrans (formerly Alcaligenes defragrans) wasgenerated by oligonucleotide concatenation to fit the codon usage of E.coli. A stretch of 6 histidine codons was inserted after the methionineinitiation codon to provide an affinity tag for purification. The genethus synthesized was cloned in a pET25b(+) expression vector (the vectorwas constructed by GeneArt AG). Competent E. coli BL21(DE3) cells(Novagen) were transformed with this vector according to the heat shockprocedure. As negative control, E. coli BL21(DE3) strain was transformedwith empty vector. The transformed cells were grown with shaking (160rpm) on ZYM-5052 auto-induction medium (Studier F W, Prot. Exp. Pur. 41(2005), 207-234) for 6 hours at 37° C. and protein expression wascontinued at 18° C. overnight (approximately 12 hours). The cells werecollected by centrifugation at 4° C., 10,000 rpm for 20 min and thepellets were frozen at −80° C.

Preparation of Cell Lysate

The pellets from 100 ml of culture cells were thawed on ice andresuspended in 4 ml of 50 mM Tris-HCl pH 7.5. 10 μl of lysonase(Novagen) were then added. Cells were incubated for 10 minutes at roomtemperature and then returned to ice for 20 minutes. Proteinconcentration was determined using the Bradford method (Biorad).

Example 2 1,3-butadiene Production from (2E)-2-buten-1-ol (trans crotylalcohol)

The enzymatic assays were carried out under the following conditions:

-   50 mM Tris HCl pH 7.5-   2 mM D,L-Dithiothreitol-   0-80 mM (2E)-2-buten-1-ol (trans crotyl alcohol)-   The pH was adjusted to 7.5

0.25 ml of cell lysate containing recombinant linalooldehydratase-isomerase was added to 0.5 ml of reaction mixture. Anenzyme-free control reaction containing lysate of E. coli cellstransformed with empty vector was carried out in parallel. Assays wereincubated at 37° C. for 1-22 hours in a 2 ml sealed glass vial(Interchim) with shaking. One ml of the headspace phase was thencollected and injected into a gas chromatograph Varian 450-GC equippedwith a flame ionization detector (FID). Nitrogen was used as carrier gaswith a flow rate of 1.5 ml/min. Volatile compounds werechromatographically separated on Rt-Alumina Bond/Na₂SO₄ column (Restek)using an isothermal mode at 130° C. The enzymatic reaction product wasidentified by comparison with 1,3-butadiene standard (Sigma). Underthese GC conditions, the retention time for butadiene was 7.6 min. Asignificant production of 1,3-butadiene was observed in enzymatic assaywith linalool dehydratase-isomerase. No butadiene signal was observed inenzyme-free control assay (FIG. 7). The turnover number for thisconversion amounted to about 3×10⁻⁵ s⁻¹ substrate molecule per enzymeactive site.

Example 3 1,3-butadiene Production from 3-buten-2-ol

The enzymatic assays were carried out under the following conditions:

-   50 mM Tris HCl pH 7.5-   2 mM D,L-Dithiothreitol-   0-80 mM 3-buten-2-ol-   The pH was adjusted to 7.5

0.25 ml of cell lysate containing recombinant linalooldehydratase-isomerase was added to 0.5 nil of reaction mixture. Anenzyme-free control reaction containing lysate of E. coli cellstransformed with empty vector was carried out in parallel. Assays wereincubated at 37° C. for 1-22 hours in a 2 ml sealed glass vial(Interchim) with shaking. 1,3-butadiene production was analyzed byGC/FID procedure as described in example 2. A significant production of1,3-butadiene was observed in enzymatic assay with linalooldehydratase-isomerase. No butadiene signal was observed in enzyme-freecontrol assay (FIG. 8). The turnover number for this conversion amountedto about 10⁻⁴ s⁻¹ substrate molecule per enzyme active site.

Example 4 2-methyl-1,3-butadiene (isoprene) Production from3-methyl-2-buten-1-ol (prenol)

The enzymatic assays were carried out under the following conditions:

-   50 mM Tris HCl pH 7.5-   2 mM D,L-Dithiothreitol-   0-80 mM 3-methyl-2-buten-1-ol (prenol)-   The pH was adjusted to 7.5

0.25 ml of cell lysate containing recombinant linalooldehydratase-isomerase was added to 0.5 nil of reaction mixture. Anenzyme-free control reaction containing lysate of E. coli cellstransformed with empty vector was carried out in parallel. Assays wereincubated at 37° C. for 1-22 hours in a 2.0 ml sealed glass vial(Interchim) with shaking. 100 μl of the headspace phase was thencollected and injected into a gas chromatograph Varian 450-GC equippedwith a flame ionization detector (FID). Volatiles compounds fromheadspace phase were separated on Rtx-1 column (Restek) using nitrogenas carrier gas with a flow rate of 1.5 ml/min. The oven cycle for eachsample was 100° C. for 4 minutes, increasing temperature at 20°C./minute to a temperature of 130° C., and hold at 130° C. for 1.5minutes. The total run time was 7 min. The enzymatic reaction productwas identified by comparison with isoprene standard (Sigma). Under theseGC conditions, the retention time for isoprene was 3.08 min. Asignificant production of isoprene was observed in enzymatic assay withlinalool dehydratase-isomerase. An insignificant signal of isoprenecorresponding to spontaneous decomposition of prenol was observed inenzyme-free control assay (Table 1). The turnover number for thisconversion amounted to about 3×10⁻⁴ s⁻¹ substrate molecule per enzymeactive site.

TABLE 1 Isoprene production after 22 hours incubation in assays with 80mM prenol . . . Isoprene Assay peak area, arbitrary units Enzymaticassay with linalool dehydratase- 29705.4 isomerase Enzyme-free controlassay 7.5

Example 5 2-methyl-1,3-butadiene (isoprene) Production from3-methyl-3-buten-1-ol (isoprenol)

The enzymatic assays were carried out under the following conditions:

-   50 mM Tris HCl pH 7.5-   2 mM D,L-Dithiothreitol-   0-80 mM 3-methyl-3-buten-1-ol (isoprenol)-   The pH was adjusted to 7.5

0.25 ml of cell lysate containing recombinant linalooldehydratase-isomerase was added to 0.5 ml of reaction mixture. Anenzyme-free control reaction containing lysate of E. coli cellstransformed with empty vector was carried out in parallel. Assays wereincubated at 37° C. for 1-22 hours in a 2 ml sealed glass vial(Interchim) with shaking. Isoprene production was analyzed by GC/FIDprocedure as described in example 4. A significant production ofisoprene was observed in enzymatic assay with linalooldehydratase-isomerase. No isoprene signal was observed in enzyme-freecontrol assay (FIG. 9). The turnover number for this conversion amountedto about 3×10⁻⁵ s⁻¹ substrate molecule per enzyme active site.

Example 6 2-methyl-1,3-butadiene (isoprene) production from2-methyl-3-buten-2-ol

The enzymatic assays were carried out under the following conditions:

-   50 mM Tris HCl pH 7.5-   2 mM D,L-Dithiothreitol-   0-80 mM 2-methyl-3-buten-2-ol-   The pH was adjusted to 7.5

0.25 ml of cell lysate containing recombinant linalooldehydratase-isomerase was added to 0.5 ml of reaction mixture. Anenzyme-free control reaction containing lysate of E. coli cellstransformed with empty vector was carried out in parallel.

Assays were incubated at 37° C. for 1-22 hours in a 2 ml sealed glassvial (Interchim) with shaking. Isoprene production was analyzed byGC/FID procedure as described in example 4. A significant production ofisoprene was observed in enzymatic assay with linalooldehydratase-isomerase. No isoprene signal was observed in enzyme-freecontrol assay (FIG. 10). The turnover number for this conversionamounted to about 10⁻³ s⁻¹ substrate molecule per enzyme active site.

The invention claimed is:
 1. A method for producing a conjugated diene comprising enzymatically converting a C_(n)H_(2n)O into C_(n)H_(2n-2)+H₂O, wherein 3<n<7, by an enzyme at least 70% identical to the amino acid sequence of SEQ ID NO:1 wherein said enzyme has alkenol dehydratase activity.
 2. The method of claim 1, wherein said method is carried out in vitro.
 3. The method of claim 1, wherein said method is carried out in a microorganism.
 4. The method of claim 1, wherein C_(n)H_(2n)O is C₄H₈O.
 5. The method of claim 4, wherein the C₄H₈O is but-2-en-1-ol, but-3-en-2-ol, or but-3-en-1-ol.
 6. The method of claim 5, wherein 1,3-butadiene is recovered.
 7. The method of claim 1, wherein C_(n)H_(2n)O is C₅H₁₀O.
 8. The method of claim 7, wherein the C₅H₁₀O is 3-methylbut-3-en-1-ol, 2-methylbut-2-en-1-ol, 3-methylbut-3-en-2-ol, or 2-methylbut-3-en-1-ol.
 9. The method of claim 8, wherein isoprene is recovered.
 10. The method of claim 1, wherein C_(n)H_(2n)O is C₆H₁₂O.
 11. The method of claim 10, wherein the C₆H₁₂O is are 2,3-dimethylbut-2-en-1-ol, 2,3-dimethylbut-3-en-2-ol and 2,3-dimethylbut-3-en-1-ol.
 12. The method of claim 11, wherein dimethyl-butadiene is recovered.
 13. The method of claim 10, wherein the enzyme is at least 75% identical to the amino acid sequence of SEQ ID NO:1.
 14. The method of claim 10, wherein the enzyme is at least 80% identical to the amino acid sequence of SEQ ID NO:1.
 15. The method of claim 10, wherein the enzyme is at least 90% identical to the amino acid sequence of SEQ ID NO:1.
 16. The method of claim 10, wherein the enzyme is the amino acid sequence of SEQ ID NO:1.
 17. A composition comprising a microorganism comprising an enzyme at least 70% identical to the amino acid sequence of SEQ ID NO:1, wherein said enzyme has alkenol dehydratase activity, and a C_(n)H_(2n)O alcohol, wherein 3<n<7.
 18. The composition of claim 17, wherein C_(n)H_(2n)O is C₄H₈O.
 19. The composition of claim 18, wherein the C₄H₈O is but-2-en-1-ol, but-3-en-2-ol, or but-3-en-1-ol.
 20. The composition of claim 17, wherein C_(n)H_(2n)O is C₅H₁₀O.
 21. The composition of claim 20, wherein the C₅H₁₀O is 3-methylbut-3-en-1-ol, 2-methylbut-2-en-1-ol, 3-methylbut-3-en-2-ol, or 2-methylbut-3-en-1-ol.
 22. The composition of claim 17, wherein C_(n)H_(2n)O is C₆H₁₂O.
 23. The composition of claim 10, wherein the C₆H₁₂O is are 2,3-dimethylbut-2-en-1-ol, 2,3-dimethylbut-3-en-2-ol and 2,3-dimethylbut-3-en-1-ol.
 24. The composition of claim 22, wherein the enzyme is at least 75% identical to the amino acid sequence of SEQ ID NO:1.
 25. The composition of claim 22, wherein the enzyme is at least 80% identical to the amino acid sequence of SEQ ID NO:1.
 26. The composition of claim 22, wherein the enzyme is at least 90% identical to the amino acid sequence of SEQ ID NO:1.
 27. The composition of claim 22, wherein the enzyme is the amino acid sequence of SEQ ID NO:1.
 28. A composition comprising an enzyme at least 70% identical to the amino acid sequence of SEQ ID NO:1, wherein said enzyme has alkenol dehydratase activity, and a C_(n)H_(2n)O alcohol, wherein 3<n<7.
 29. The composition of claim 28, wherein C_(n)H_(2n)O is C₄H₈O.
 30. The composition of claim 29, wherein the C₄H₈O is but-2-en-1-ol, but-3-en-2-ol, or but-3-en-1-ol.
 31. The composition of claim 28, wherein C_(n)H_(2n)O is C₅H₁₀O.
 32. The composition of claim 31, wherein the C₅H₁₀O is 3-methylbut-3-en-1-ol, 2-methylbut-2-en-1-ol, 3-methylbut-3-en-2-ol, or 2-methylbut-3-en-1-ol.
 33. The composition of claim 28, wherein C_(n)H_(2n)O is C₆H₁₂O.
 34. The composition of claim 33, wherein the C₆H₁₂O is are 2,3-dimethylbut-2-en-1-ol, 2,3-dimethylbut-3-en-2-ol and 2,3-dimethylbut-3-en-1-ol.
 35. The composition of claim 28, wherein the enzyme is at least 75% identical to the amino acid sequence of SEQ ID NO:1.
 36. The composition of claim 28, wherein the enzyme is at least 80% identical to the amino acid sequence of SEQ ID NO:1.
 37. The composition of claim 28, wherein the enzyme is at least 90% identical to the amino acid sequence of SEQ ID NO:1.
 38. The composition of claim 28, wherein the enzyme is the amino acid sequence of SEQ ID NO:1. 